1. Field of the Invention
This invention relates to a chemical assay tape for determining the quantity of a specific substance in a body fluid (e.g. blood, serum, urine, etc) of an organism or the like.
2. Description of the Prior Art
Determination of the amounts of various metabolites in body fluids, e.g. glucose, bilirubin, urea, uric acid, cholesterol, lactic dehydrogenase, creatine kinase, GOT, GPT, etc, is clinically important and essential to the diagnosis of diseases, follow-up studies of medical treatments, prognoses and the like. In a clinical chemical test in which blood or the like is used as a sample, it is desirable to conduct a highly accurate test by using a very small quantity of a liquid sample. Although a so-called wet method employing a solution reagent has been used widely, tests using this method cannot be conducted as quickly as would be desirable.
As a means for quickly conducting a highly accurate test by using a very small quantity of a liquid sample, chemical assay slides have been developed by utilizing dry-type multilayer films. There are various types of the chemical assay slides according to their layer structures.
An example of types of assay slide is a dry-type, multilayered film sandwiched between a pair of plastic frames. An opening into which a liquid sample may be deposited is formed in the center of the upper frame, while an opening through which optical measurements can be made is formed in the lower frame. The multilayered films are composed of a transparent support, a reagent layer, a reflection layer, and a spreading layer. The transparent support is, for example, a subbed, thin plastic film. The reagent layer, coated on the transparent support contains a reagent which reacts with a substance contained in a liquid sample, and after the reaction, the reagent layer exhibits an optical density, the value of which depends on quantity of the substance which was originally contained in the sample. The reflection layer prevents the light incident on the reagent layer from reaching the spreading layer, so that the liquid sample supplied to the spreading layer is not optically detected. In the spreading layer, the deposited liquid sample uniformly spreads over an area which is substantially proportional to the quantity of the deposited liquid sample.
In order to determine the amount of a substance contained in a liquid sample by using such a chemical assay slide, a predetermined amount of the liquid sample, e.g. whole blood, is spotted onto the surface of the spreading layer through the opening of the upper frame. The blood spreads into the spreading layer and passes through the reflection layer to reach the reagent layer where it reacts with the reagent to form a product having a specific color, hereinafter sometimes called a colorant. After the deposition of the liquid sample, the chemical assay slide is maintained at a constant temperature for an appropriate period of time so that the color reaction, i.e. the reaction forming a product having a specific color, advances sufficiently. Then, the reagent layer is illuminated with light through the opening in the lower frame. The amount of reflected light in a predetermined region of wavelength is measured so as to determine the optical density of reflection. The amount of the substance in question is determined on the basis of a curve indicating known optical density versus sample component quantity which was obtained prior to the deposition of the sample liquid.
Such a chemical assay slide can be prepared for each substance which is to be subjected to assay, but this may lead to rather disadvantage in view of the expense involved. Firstly, the process for manufacturing chemical assay slides may be laborious. In order to mass-produce the chemical assay slides, a sheet of film having a large area is made and then cut into small pieces. Thereafter, each piece is fixed to a frame so that a chemical assay slide is formed. It may be particularly laborious to cut out film pieces having a precise size and to fix them accurately to the frame. Although the manual labor required can be reduced by using an automatic machine, considerable investment and maintenance are required therefor. Secondly, the material for the frame and the processing thereof for finishing the slide may be costly.
By configuring the chemical assay film as a long tape, the labor and cost required to produce a slide for each sample can be eliminated.
Chemical assay tapes are mentioned, in combination with analysis apparatuses, in U.S. Pat. No. 3,260,413, U.S. Pat. No. 3,526,480, and U.S. Pat. No. 3,992,158. However, as stated in U.S. Pat. No. 3,992,158, the analysis apparatuses disclosed in U.S. Pat. No. 3,260,413 and U.S. Pat. No. 3,526,480 have a complicated structure in which two or more tapes are temporarily brought into contact with each other to form a composite and then separated from each other. U.S. Pat. No. 3,992,158 states that the chemical assay tapes in accordance with that patent are advantageous in that a complicated apparatus is unnecessary and that assay tapes of different types can be used simultaneously or successively.
However, when the integral multilayered assay tape disclosed in U.S. Pat. No. 3,992,158 is formed as a long tape and wound up in a roll so that the tape can be received in a container or continuously supplied to an analysis apparatus, the spreading layer, which is composed of a non-fibrous porous medium, often cracks.
The multilayered assay film disclosed in U.S. Pat. No. 4,292,272 has a spreading layer made of a fibrous porous medium. Thus, the spreading layer does not crack easily. However, when a porous layer, e.g. a filter layer, is disposed between the spreading layer and the reagent layer, the porous layer often cracks during the manufacture of the film or the handling of the film for an assay. The cracked portion cannot be used for assay of a liquid sample. For example, during the manufacture, while a multilayered chemical assay film having a porous filter layer between a spreading layer and a reagent layer is dried in vacuum in order to control the moisture content, the filter layer or the like often cracks.